A conventional type of semiconductor device may have the following arrangement. Specifically, the semiconductor device includes partially overlapped lead terminals extending in the opposite directions, a semiconductor element (chip) interposed between the partially overlapped lead terminals, and a mold member made of synthetic resin for packaging the semiconductor element together with the members around the semiconductor element. The applicant of the present invention disclosed a lead frame used for making the semiconductor device of the above type in Japanese Patent Publication Nos. 6-36422 and 6-71015. The conventional lead frame is shown in FIGS. 27-29 of the accompanying drawings of this application.
The conventional lead frame 20 includes at least two elongated side frames 21, 22 extending in parallel to each other, and section bars 23 connecting the side frames 21, 22 at predetermined intervals. Each section bar 23 has two joint portions 23a having a relatively small width. Thus, the side frames 21, 22 can be shifted longitudinally with respect to each other. The side frame 21 is formed with a plurality of first lead terminals 24, while the side frame 22 is formed with a corresponding number of second lead terminals 25. The free end portions of the paired first and second lead terminals 24, 25 are arranged close to each other. The side frames 21, 22 are provided with engaging holes 26 at predetermined intervals. These holes are brought into engagement with sprockets (not shown) used to move the side frames 21, 22 longitudinally thereof.
The semiconductor device D is made through the following steps:
1 A semiconductor element T is bonded to the free end portion 24a of the first lead terminal 24;
2 By moving the side frames 21, 22 at different rates, the free end portion 25a of the second lead terminal 25 is put on the semiconductor element T which is bonded to the first lead terminal 24;
3 The free end portion 25a of the second lead terminal 25 is bonded to the semiconductor element T by soldering, conductive adhesive, or pressure welding for example;
4 With their free end portions 24a, 25a overlapped, the lead terminals 24, 25 are moved to a synthetic resin molding section, at which the semiconductor element T together with other members around the semiconductor element is enclosed by a mold member M of synthetic resin, as indicated by single-dot chain lines in FIG. 29; and
5 The lead terminals 24, 25 are cut off at their joint portions after continuity across the terminals is inspected.
According to the prior art, a plurality of semiconductor devices D can be made using a single lead frame 20. Thus, the manufacturing efficiency of the semiconductor devices D is remarkably improved.
In accordance with the above prior art, the section bars 23 are deformed when the side frames 21, 22 are shifted longitudinally. However, the joint portions 23a of each section bar 23 do not entirely undergo plastic deformation but are subjected to elastic deformation to some extent. Thus, due to restoring force from the spring-back action of each section bar 23, the side frames 21, 22 are urged toward the initial positions the frames were held in before the shifting operation. Consequently, the lead terminals 24, 25 are slightly bent. As a result, the elastic force of these terminals 24, 25 may work to cause the lead terminals to be detached from the semiconductor element T, which leads to defective products with improper electrical continuity.
One way to deal with the above problems may be to move the side frames 21, 22 without providing any play between the sprocket and the engaging holes 26. In this way, the spring-back action of the section bars 23 may be completely restrained. In practice however, it is difficult to eliminate the play between the sprocket and the engaging holes 26. Thus, conventionally the defective connection due to the spring-back of the section bars 23 was not completely prevented.
The above problems become more serious in an instance where more than one second lead terminals (corresponding to a single first lead terminal) are bonded to a semiconductor element. Specifically, when use is made of a lead frame provided with a single first lead terminal and more than one second lead terminals to be bonded to a single semiconductor element, the rigidity of the lead terminals put together is increased. Thus, the strength of the detaching force to act on the bonding region between the lead terminals and the semiconductor element is increased. As a result, more lead terminals may be unduly detached from semiconductor elements, thereby increasing the number of defective products.